Hi I have installed sys-fs/udev-151-r4  USE="extras -devfs-compat
-old-hd-rules (-selinux) -test" on an almost clean hardened stage3 and I
found that after rebooting it won't run. It could be a problem of the
.config but turns out it runs and works like a charm when started
manually. So my question is, what could be happening? How can I fix it?

FWIW the system uses baselayout-1